Hundreds of Britons accused of being paedophiles in the country's biggest Internet child pornography investigation were actually victims of credit card fraud, it was claimed last night.

More than 7,000 - including rock star Pete Townshend - were said to have downloaded child-porn images from a U.S. website.

But an investigation has found that many of those charged as part of the police inquiry codenamed Operation Ore were innocent and their card details had been used illegally.

Simon Bunce, who was accused of using the Texas-based Landslide website, said he was certain his personal information had been used fraudulently. Police found no evidence on his computer but his credit card details were found on the site.

"Thirty-nine people committed suicide after being accused of what I was accused of," he said. "I reacted in a different way. I investigated it diligently and I established I was the victim of credit card fraud."

The case against Mr Bunce was dropped after six months.

In another case, a father and son were investigated for a year. Nothing was found on their computer but their card details had been used. They recently found out they would not be prosecuted.

Makers of the BBC Radio 4 programme The Investigation, which was broadcast last night, interviewed Ross Anderson, professor of security engineering at Cambridge University, who was a defence expert witness in several Operation Ore trials.

"Police just didn't look far and didn't understand the evidence of wholesale card fraud," he said.

"As a result hundreds, possibly even thousands, of people have been put through a terrible mill with threats of prosecution for child pornography and all the rest of it when in fact they had nothing to do with child pornography."

Police admit some of the 7,200 on a list supplied to them by U.S. officials were victims of card fraud but say they were not prosecuted and that they do not believe fraud was rife on the website. So far, 2,300 people have been found guilty of offences.

Jim Gamble, former head of the National Crime Squad who is now head of the Child Exploitation and Online Protection Centre, said: "Over 90 per cent of those involved pleaded guilty. That's not about credit card fraud.

"That's people who have had the allegation levelled against them. The evidence has been collected. And they at court have said, 'I'm guilty of this offence'."

Those held in Operation Ore, which was launched in 2002 and cost £10 million, included Pete Townshend of The Who, Ronnie Barker's son Adam and numerous police officers.

Townshend denied that he was a paedophile, claiming he only accessed a site as research for an anti-child pornography campaign and for his autobiography.

He was not charged, but accepted a police caution and was placed on the sex offenders' register for five years.

Adam Barker went on the run and has never been traced. At least 38 suspects are known to have committed suicide. Of these, 34 had illegal images on their computers.